The FX9 is physically very similar to the FS7 and is easily mistaken for it at a distance, however it is supposed to have all new electronics inside. The menus are similar to the FS7 but improved. The controls have been moved to make it easier to operate when on the shoulder. It uses more power than the FS7. It will have a new version of the XDCA. It supports the XQD cards, you may have. It will work with any rigs you have for the FS7. There is support for Genlock (without the new XDCA) but that may not be delivered until a firmware update.
With the new XDCA the Camera will support 16 bit raw.
Note: this is a new Camera and Sony may talk about things now that are not delivered until a subsequent firmware update. So check before you buy.
The FS7 became the Indie camera of choice, certainly if you believe the Televisual survey of most rented cameras. It earned the title of “workhorse” because it was the most trusted. TV production does use all the other industry cameras, however the FS7 hit budget friendly price point. The FX9 may well earn that role. Venice could do better but it also requires a bigger budget.
The FX9 has a 6K chip, however it is 4K when you get essence from the Camera.